1. Technical Field
The present disclosure relates to a wireless communication system, a wireless control method, and a virtual base station apparatus for performing millimeter-wave band communication using beamforming.
2. Description of the Related Art
In recent years, to ensure a bandwidth of 1 GHz or higher to meet rapidly increasing traffic demands, studies have been made on the employment of small base station apparatuses that perform communication by using millimeter wave bands. For example, a communication system (also sometimes referred to as a heterogeneous network) is conceived in which a plurality of small base station apparatuses are located within a communication area for a base station apparatus that performs communication by using microwave bands.
With the use of millimeter wave bands, such small base station apparatuses have propagation loss greater than with the use of microwave bands, resulting in it being difficult to extend the arrival range of radio waves.
One of the schemes contributing to at least one of addressing such experience of propagation loss, the increase in communication speed, and the spreading of the cell area is directional control (beamforming) for a base station apparatus and a terminal (also sometimes referred to as a “terminal apparatus” or “station (STA)”) by using a plurality of antenna elements (antenna array). In transmission using directional control, a transmitting apparatus (base station apparatus or terminal) directs radio waves to be transmitted toward a communication partner, thereby allowing the radio waves to reach locations farther than those in non-directional transmission. This allows the transmitting apparatus to extend the cell area that is covered. In addition, since directional control enables enhanced signal to interference-plus-noise power ratio (SINR), the application of a modulation scheme and coding rate with high frequency use efficiency allows the transmitting apparatus to perform communication at high transmission speeds (see, for example, Institute of Electrical and Electronics Engineers (IEEE) 802.11ad-2012 Standard for Information Technology—Telecommunications and Information Exchange between Systems—Local and Metropolitan Area Networks—Specific Requirements—Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications Amendment 3: Enhancements for Very High Throughput in the 60 GHz Band).
In a wireless network that uses millimeter wave bands, it is necessary for a base station apparatus to perform beamforming training for directivity matching for each terminal to be connected. The base station apparatus needs to have directivity (scan) over a wider angle to increase the cell area that is covered, and the time required for the beamforming training becomes overhead, resulting in a reduction in frequency use efficiency.